Manner by which something functions; the workings.(noun)
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Use "functioning" in a sentence
"After they removed her pancreas, they extracted its islet cells and implanted them into her left forearm, creating what they call a functioning pancreas in her arm."
"Why is the term 'functioning' alcoholic acceptable, but, if one couples the word functioning with other things, it's sacrilege?"
"Psychologists and neuropsychologists test memory, attention, language and information processing to assess brain functioning and the need for intervention."